Metal tubing is commonly used for both structural elements and for pipelines to transport materials, with selection of the specific metal or alloy dependent on the required material properties and cost effectiveness. Unfortunately, most metals are susceptible to corrosion processes, especially when exposed to water, salts, acids, and/or air. This is especially true of most types of steel. If uncontrolled, corrosion can lead to loss of structural integrity. As a result, a wide range of technologies have been developed to prevent, monitor, and/or control corrosion of metallic structures.
In some applications, a metal pipeline passes through a second metal pipe or conduit called a casing. The casing typically provides protection to the inner pipeline. Problems arising from corrosion can be particularly challenging in casing applications due to the range of corrosion processes that can occur individually and synergistically with the casing and the pipeline. A number of approaches have been attempted to prevent or control corrosion in such situation.
Metal pipe, conduit, and casing may have a permanent protective coating applied to interior and/or exterior surfaces to prevent corrosion. Urethane or epoxy based coating products are commonly used. This approach is generally effective, but corrosion can still initiate at any defects in the coating and migrate under the coating.
Cathodic protection is another approach often applied to pipelines and other metallic structures. Cathodic protection controls the corrosion of a metal surface by making it the cathode of an electrochemical cell. Impressed current cathodic protection and galvanic cathodic protection are the two types of cathodic protection techniques that are typically used to control the external corrosion on pipelines. The effectiveness of cathodic protection can be reduced by electrical contact between the protected structure (the carrier pipe) and other metals (e.g. the pipe casing). Therefore, non-conducting “spacers” are frequently used to prevent such electrical contact between the pipe and the casing. The casing may be vented to the atmosphere, but is otherwise usually sealed to the external environment to prevent incursion of air or water into the interstitial space between the pipe and the casing.
A passive approach to corrosion inhibition of the carrier pipe involves filling the interstitial space with a highly dielectric material to physically exclude air and water and to improve the electrical separation between the pipe and the casing. Common commercial filler products are generally petroleum based compositions containing wax; examples include STOPAQ™ Casing Filler (Stopaq BV), Royfill Hot Fill and Royfill 404-B (both from the Chase Corporation, Royston Laboratory Division), and Trenton Fill-coat #1 (The Trenton Corporation). Another example is described in U.S. Pat. No. 4,925,616 regarding compositions based on tall oil pitch. For most of the above products, the material must be heated for injection into the interstitial space; which adds to the cost and complexity of installation. Also, any voids or defects in the filling have the potential to compromise the corrosion protection, through action of entrained moisture and oxygen on the carrier pipe surface. While the above filler materials tend to be relatively non-toxic and non-hazardous, they are still fairly difficult to remove and clean-up, as they are viscous to solid at ambient temperatures and are not water soluble.
The above fillers are typically dielectric and shield the carrier pipe from the benefits of cathodic protection current applied to the pipe casing. Corrosion inhibitors may be added to these filler formulations to reduce corrosion on the carrier pipe but the long-term effectiveness of the corrosion inhibitors may be questionable due to the high temperature of the filler during the initial installation process, which can degrade the corrosion inhibitors, and the restrictions of inhibitor migration through the dielectric filler materials.
Thus, there remains a need for materials that can provide pro-active corrosion protection as an electrically conducting volume filler in the interstitial space between a pipeline and the casing to permit cathodic current flow from the pipe casing to the carrier pipe.
It is therefore an object of the present invention to provide an electrically conducting volume filler for application between spaced-apart metallic articles to convey cathodic protection current from the first metallic article (or article portion) to the second metallic article (or article portion).
It is a further object of the present invention to provide a volume filler for placement in the interstitial space between a pipeline and is casing, which volume filler promotes corrosion inhibition of both the pipeline and the casing.
It is another object of the present invention to provide a volume filler with active corrosion inhibiting agents dispersed therein, which filler may be easily installed in the space between corrosion-susceptible articles or article portions.
It is a yet further object of the present invention to provide a corrosion inhibiting volume filler that is inexpensive, non-hazardous, easy to apply, and easy to remove and/or clean up.